The present invention relates to a copier, printer, facsimile transceiver or similar equipment for copying or printing an image by an electrophotographic procedure and, more particularly, to an electrophotographic process control device capable of controlling an electrophotographic process on a step basis.
A traditional method of controlling an electrophotographic process consists in measuring the surface potential of a photoconductive drum and the image density, i.e., the amount of toner deposition by an electrometer and a photosensor, respectively, and selecting optimal manipulation amounts matching the respective measured values by referencing a look-up table which is prepared beforehand by experiments. Another conventional method is to change manipulation amounts of various sections of equipment and determine, by a PID (Proportional Integrated Difference) or similar scheme, optimal manipulation amounts while feeding back the resulting states of the equipment sensed by sensors. Still another and more advanced method uses a computing unit implemented with a fuzzy estimation algorithm and manipulates various subjects of control on the basis of the total decision of numerous parameters entangled in a complicated way. Such conventional control methods have various problems left unsolved, as enumerated below.
(1) Causes of the fluctuation of developing ability are too complicated to be presented as a model for control.
(2) Many of the parameters cannot be directly measured, e.g., the charging ability of a toner and the come-off of the coating of a developer as well as the spent condition of a developer.
(3) Since the response of toner supply delays a period of time associated with several copies, the consumption of toner which is continuous and great in amount cannot be readily dealt with.
(4) A huge amount of experimental data is needed in the event of the design and development of a developing unit.
(5) When a reference image pattern is formed to measure the density thereof, the copying speed is lowered and, in addition, the load acting on a cleaning unit is increased.